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Community and Q&A

Basement Ventilation

pjpfeiff | Posted in Mechanicals on

Climate Zone 4
I have an unconditioned basement that I would like to vent to freshen the air.  Despite being unconditioned it stays a nice enough temperature, so I had wanted to use a couple LUNOS e2s to not ruin that.  However, there isn’t enough above-grade wall to install those (~14″ of block + 2″ sill plate + 7.5″ rim joist).

Any suggestions?  I have half mind to install Lunos in an unrecommended manner, but that could be an expensive mistake.  Am I crazy to want an ERV/HRV down there?  Even if I don’t use heat recovery, using balanced ventilation seems ideal so that I am not (a) bringing conditioned air down into the basement and exhausting it or (b) pushing air into the basement and making it migrate upstairs.  Note that the basement door must remain partially open for the cats to get to their litter box (which is one reason why I want ventilation).

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  1. user-2310254 | | #1


    What are you trying to accomplish by "freshening" the air? Is there a damp/humid smell in the basement?

    1. Expert Member
      NICK KEENAN | | #2

      "Note that the basement door must remain partially open for the cats to get to their litter box (which is one reason why I want ventilation)."

      1. pjpfeiff | | #3

        Haha, thanks. Yeah, it's probably the main reason, actually for most of the basement. There is also a small room in that only has a gravel floor which is a little musty, so it would be nice to exchange out some of that air too. And also whatever residual reduction in radon we get from it would be nice, but our levels upstairs aren't bad enough to require mitigation.

        1. Expert Member
          NICK KEENAN | | #4

          The danger with ventilating basements is if you live in a place with humidity you're just bringing in more moisture.

          A sheet of plastic over the gravel floor will make a noticeable difference.

          If you are trying to get rid of odors you want to vent out from the basement and pull upstairs air down. If you pull basement air up it will bring the odor into the rest of the house. But I wonder if there are better ways to deal with point odor sources.

      2. Expert Member
        BILL WICHERS | | #5

        I would put a small bathroom exhaust fan in the room or immediate area of the cat box and let it run continuously. Unless you have a a very well sealed house, that's probably all you need. If you do have a well-sealed house, you might need makeup air too.

        How much you want to get rid of cat box smell is a matter of preference :-) You might also try changing the type of cat litter you use. I found that the clay stuff made dust that would make me sick, so I changed to "world's best" brand cat litter which is made from crunched up corn cob material. MUCH less dust. I'll never go back! There is also "yesterday's news" brand (and some similar produces by other names), which is a sort of extruded recycled newspaper material. I'd try a few and see if you can get the improvement you want without adding active ventilation. You can always add ventilation later if changing litter materials doesn't help.


        1. pjpfeiff | | #7

          Thanks, I've tried the newspaper-based one when one of the cats had an ingrown claw removed. The cats didn't really care for it. I'll check out the "world's best" sometime. A bathroom fan does seem like the easiest ventilation option. However, can you put a 4" hole in a 7.25" rim joist? (Never mind that my original plan would have involved a 6.5" hole)

          1. Expert Member
            Akos | | #9

            I've done exactly this for my sister (exhaust fan for kitty litter). Try to find a smallest bathroom van you can. You only need 20 to 40 CFM, so you can use 3" pipe (or run 4" pipe but step down to 3" just before the wall). Much smaller hole and no problem through the joist. Just don't do it above a basement window. Might be worth to add a damper in the duct so you can adjust the flow, you only need enough to keep the smell at bay.

  2. Expert Member
    Peter Engle | | #6

    Something like a Humidex exhaust fan would work. I don't particularly like their equipment, and I hate their marketing, but the idea works. It's basically an exhaust-only ventilation system, with the inlet at the basement floor. In theory, it takes the coldest & heaviest (and smelliest) air off the basement floor, pulling cleaner, dryer, warmer air from above. This will dry out the basement and vent the odors at the cost of potentially increasing the overall air infiltration rate of the house. The Humidex people swear this doesn't happen, but that constant exhaust has to come from somewhere....

    1. pjpfeiff | | #8

      Thanks, I found something similar, and I had the same thoughts. It actually seems like a good idea...just not as good as they make it out to be. I wonder if I could get 90% of the benefit by putting a bathroom fan on some legs just above the floor and running duct up and out of the basement.

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